Extruder Clicking & Feeding Issues

A rhythmic clicking sound from the extruder means the motor is trying to push filament that isn't moving — the gear is skipping teeth against the filament instead of feeding it. Left unaddressed, this grinds a flat spot into the filament and eventually stops feeding entirely.

Most common causes, in order of likelihood

Clogged or partially clogged nozzle. Molten plastic can't escape fast enough, backing pressure up through the whole path. Try a cold pull: heat the nozzle to printing temp, then let it cool to about 90°C while pulling firm steady pressure on the filament — the frozen plug should pull free from the nozzle.
Idler tension too tight or too loose. The spring-loaded idler arm on the extruder needs enough pressure to grip filament without crushing it. Too tight and soft filaments (like flexibles) get squished flat; too loose and the gear can't grip firmly enough.
Temperature too low for the filament/speed combination. If you've upgraded to faster print speeds without raising temperature to match, the hotend may not be melting filament fast enough.
Dirty or worn extruder gear. The stock brass extruder gear can accumulate ground-up filament dust in its teeth over time — remove and clean it with a small brush.
Tangled or snagged filament spool. Check the spool itself before assuming it's a printer problem — filament that's crossed over itself on the spool can bind and create resistance that looks identical to an extruder fault.

Diagnosing which one it is

Release the idler lever and try pulling filament through by hand with the hotend at temperature. If it won't extrude freely even by hand, the clog is downstream of the extruder (nozzle) — not the extruder itself.
If filament extrudes fine by hand but the extruder still clicks under motor power, suspect idler tension or gear grip.

Warning: If you see a shiny groove worn into the side of the filament, stop and back the idler tension off slightly, then retry — continuing to print will only make the groove worse and can create a lower-pressure feed that leads to intermittent under-extrusion mid-print.

For deeper diagnosis of the resulting print artifacts, see Common Print Quality Problems & Fixes.